A side turn signal lamp mounted on a side mirror of an automobile is known. For example, in a side turn signal lamp 51 shown in FIG. 10, a light guide lens 53 is provided on a front surface side of a mirror housing 52, and a base end of the light guide lens 53 is provided with an LED light source 54. A distal end of the light guide lens 53 curves toward the rear of the vehicle, and a curved portion is formed with a functional light distribution portion 56 including a plurality of steps 55. The steps 55 diffuse light from the LED light source 54 sideward of the vehicle to form a light distribution pattern that conforms to laws and regulations.
Japanese Patent Application Laid-Open (Kokai) No. 2006-114309 (JP 2006-114309) proposes art for a side turn signal lamp having a curved shape similar to that in FIG. 10. In the side turn signal lamp, a reflective wall is provided rearward of a light guide lens to reflect light leaking from the lens in front of the vehicle, thereby increasing an amount of luminance at the front surface of the light guide lens. U.S. Patent Application No. 2006/193144 (US2006/193144) proposes art for a side flash lamp provided with a front cover that covers a light guide lens. In the side flash lamp, a number of steps are arranged at narrow intervals on both a front surface and a rear surface of the bar-shaped light guide lens in a longitudinal direction of the lens, so that the entire light guide lens is uniformly illuminated.
In the side turn signal lamp 51 of FIG. 10 and JP 2006-114309, the majority of light radiated from the LED light source 54 passes through the light guide lens 53 in the longitudinal direction, and is emitted from the functional light distribution portion 56. Therefore, as shown in FIG. 11, a design light distribution portion 58 darkens between the functional light distribution portion 56 and a light source side light-emitting portion 57, worsening the appearance from the front of the vehicle. In the case of the side flash lamp described in US2006/193144, since light from the LED light source is almost uniformly distributed over the entire light guide lens, the design light distribution portion is bright. However, the amount of light guided to the functional light distribution portion accordingly decreases, such that the functional light distribution portion darkens, and in particular, visibility from the side of the vehicle worsens.